Household refuse and clarifier sludge are continuously generated in practically all municipalities and represent disposal problems. the storage of household refuse during the summer months for utilization as a fuel in the winter months is not possible or practical from an environmentally sound point of view since the storage of household refuse (garbage) in the region of the source raises sanitary problems. Nevertheless household refuse does constitute an effective fuel, allowing the recovery of considerable amounts of thermal energies.
Obviously, if combustion can be carried out at some distance from the source of the fuel, the sanitary problem can be partly alleviated although transportation and handling problems and costs arise.
It is, therefore, known to sort household refuse, to dry the combustible portion thereof and to pelletize or otherwise produce components of the refuse which can be burned.
These pretreatments of household refuse are expensive at least in part because they require external energy sources and may be produce flue gases or fumes which must be cleaned before they are released into the atmosphere. The gases or fumes must be freed from smoke particles and any toxic or noxious components by the cleaning treatment.
Another treatment which may be utilized even in the summer months is the pyrolytic transformation of refuse into oil and gas, thereby at least partially utilizing the refuse in a fuel production process. These processes require highly expensive gas cleaning, oil cleaning, waste air cleaning and waste water cleaning operations.
Furthermore, it has been proposed to generate useful fuel or fuel products by pyrolyzing a mixture of refuse and so-called waste coal, a product also known as ballast coal. In this case, gas and oil may be recovered and the solid waste may be an ash which is readily disposable by dumping at waste disposal sanitary-fill sites.
Coal, waste coal/refuse and other pyrolytic gasification processes have been proposed in which the coal and refuse are pyrolyzed in a pyrolysis stage to produce a pyrolysis coke which has practically all of the heat value of the starting materials and which can be utilized effectively in combustion processes, e.g. in fossil-fuel power plant combustion.
In this case, the waste and/or mixtures of waste with coal can be continuously processed to transform the waste into gas or into a solid fuel or other combustibles which can participate in the combustion operation together with coal in the firebox of the power plant. This system has, however, the disadvantage that it requires a continuous utilization of the intermediate product such as gas and oil which may be formed by pyrolysis and does not permit storage of a combustible for later use.